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How Much Memory Minimum for Virtual OSes?

I want to run a virtual Linux OS desktop and small VoiP server from my dedicated server (which,right now, runs, CentOS 5.3.i386) and a virtual windows vista 32 desktop from one of my VPS' (which runs CentOS 5.3 x64) to my Vista 64 desktop. The servers are offsite.

I can still upgrade the servers, if necesary and within budget and I'm in a position to install my VPS and server OS and configure them appropriately for these uses. So I'm exploring what I'll need now.

On the dedi, I'll be running DNS, mail, webmail, file and webserver (obviously) for several websites and blogs as well as a number of email addresses.

On the VPS, I'll be running a DNS, webmail, mail and file server as well as secure data backup server. There will be no websites or blogs on this site.

How much memory, minimum do I need to run theses virtual instances and everything else I need to run with service degradation? Are there ways I can maximize memory without increasing physical memory? Does partitioning the hard drives make a difference in how memory works on the servers? What about virtualisation software? (I want open source, preferably, but not terribly hard to configure.) I need that which does hardware virtualization so I can use a secure VNC to connect to the servers since few do that natively and have have virtualization features.

The responses that will be most helpful to me will be solutions-oriented, scalable (to a single individual) and immediately actionable but that assumes this can all be done with the right hardware and software, not tells me why it can't without telling me how it can. I prefer to hear from those who are either doing something similar and/or have professional or serious hobbyist expertise in virtualization, related software and hardware software and server configuration.

To be safe I'd get at least 2 gigs, but the more the better when it comes to virtualization. Have to remember your host OS requires ram too, and I'd give it at least 512 free, if, 1GB.

At home my main server also runs VirtualBox and has 8GB of ram. I have about 7 VMs running smoothly. The only way to make that server choke is if I fire up my vista VM, but that will make any PC cry for more ram and cpu.

To be safe I'd get at least 2 gigs, but the more the better when it comes to virtualization. Have to remember your host OS requires ram too, and I'd give it at least 512 free, if, 1GB.

At home my main server also runs VirtualBox and has 8GB of ram. I have about 7 VMs running smoothly. The only way to make that server choke is if I fire up my vista VM, but that will make any PC cry for more ram and cpu.

Thank you. This is VERY helpful because I'm thinking I want to run Vista VMs from a Windows 2008 virtual server but you're saying that will eat up RAM and CPU? Even at 8G of RAM?

I guess running Windows VMs on a VPS with only 512MB or 1GB of RAM is out, then. Do you know if what kind of RAM a Linux VM running CentOS 5.3 VPS would take? i'm sure at least 512MB of RAM.

I may be moving my dedi service and will probably get a 64bit OS instead of the 32bit I have now. Perhaps I should have at least 4GB of RAM and run the Windows VMs from that.

If you don't mind, I'd like some more information about your own setup. What kind of CPU speed, etc. do you have on your server? Did you do anything special to prepare it for your VMs? And why VirtualBox over, say VMware server? What kinds of VMs are you running on your server?

I hope I haven't asked too many questions. Very few people seem to know about this subject well enough to provide cogent information and actionable answers to my questions.

128 mb ram is the absolute minimum but this will be very unstable and will not run many applications ect. your best bet is to go for about 512mb or 1 gig ram this ensures that you can run all the software needed, because you are wanting to run windows vista this really need 1 gig or more because vista is quite demanding.

Processor wise you're fine, bumping up to 4GB or even better, 8GB of RAM would be advised. If you plan on running 3+ VM's that get used fairly often, I would suggest getting some form of RAID to alleviate the disk I/O issues. Currently I run several semi-production boxes on $199 Dell servers (dual core 1.8GHz, 4GB) with 2-4 VM's each. Every single machine has the same issue--disk I/O. The one machine that I've setup to a SAN (with RAID5) is performing beautifully, it's even running 6 VM's without any performance detriments.

I want to run a virtual Linux OS desktop and small VoiP server from my dedicated server (which,right now, runs, CentOS 5.3.i386) and a virtual windows vista 32 desktop from one of my VPS' (which runs CentOS 5.3 x64) to my Vista 64 desktop. The servers are offsite.

I can still upgrade the servers, if necesary and within budget and I'm in a position to install my VPS and server OS and configure them appropriately for these uses. So I'm exploring what I'll need now.

On the dedi, I'll be running DNS, mail, webmail, file and webserver (obviously) for several websites and blogs as well as a number of email addresses.

On the VPS, I'll be running a DNS, webmail, mail and file server as well as secure data backup server. There will be no websites or blogs on this site.

How much memory, minimum do I need to run theses virtual instances and everything else I need to run with service degradation? Are there ways I can maximize memory without increasing physical memory? Does partitioning the hard drives make a difference in how memory works on the servers? What about virtualisation software? (I want open source, preferably, but not terribly hard to configure.) I need that which does hardware virtualization so I can use a secure VNC to connect to the servers since few do that natively and have have virtualization features.

The responses that will be most helpful to me will be solutions-oriented, scalable (to a single individual) and immediately actionable but that assumes this can all be done with the right hardware and software, not tells me why it can't without telling me how it can. I prefer to hear from those who are either doing something similar and/or have professional or serious hobbyist expertise in virtualization, related software and hardware software and server configuration.

Thank you.

April

According to my experience with KVM and (qemu-system-x86_64), 2gigs is just fine. Im running 32bit host OS so it cannot allocate more than 2gigs per VM. However with PAE your 32bit host OS is able to use fully 16gigs easily. Only limit is that 2gigs max. per VM or a process.